Recently, an electric vehicle (i.e., EV) and a hybrid vehicle (i.e., HV) have a structure for generating a small noise. Thus, it is difficult for a pedestrian to find these vehicles approaching the pedestrian. In order to increase a recognition degree of the vehicle disposed near and around the pedestrian or the like, the vehicle approach alert device for generating artificial engine sound is mounted on these vehicles (see, for example, Patent Literature 1). In the vehicle approach alert device, a method for outputting sound is a method for outputting the sound by setting a coded data, which is prepared by converting and coding the output sound data such as PCM data (i.e., pulse code modulation data) stored in a memory of a microcomputer, i.e., converting and coding the magnitude of the sound to a data code, into a D/A converter and a PWM output device. An output of the oscillating driving sound by the vehicle approach alert device is performed when a road noise is small and the vehicle speed is low.
The output sound data mainly indicates a pseudo travelling sound such as a pseudo engine sound and a pseudo motor sound. The data is stored in the memory as data for a predetermined time interval. The vehicle approach alert device outputs the data for the predetermined time interval repeatedly, so that the device outputs the approach alert sound. The output sound data presents a chord sound prepared by synthesizing multiple frequency components. The chord sound includes “fluctuation (i.e., envelope)” of sound indicated as a curve drawn by peaks of the sound or the electric waveform, i.e., “harmonization and intonation of vibrato” for increasing and decreasing a sound volume with time, so that a pedestrian easily notices approach of the vehicle through the chord sound.
However, since the output sound data is presented by adding the “fluctuation,” the amount of time for the output sound data to be stored, i.e., the length of time for the output sound data increases, and therefore, the memory capacity increases. Further, the memory capacity of the microcomputer limits the time interval, and therefore, it is not sufficient to add the “fluctuation” of sound such as “harmonization and intonation of vibrato” to be output.
Furthermore, even if the “fluctuation” is added into the output sound data, the way of hearing the approach alert sound by the pedestrian may be changed according to a mounting place of the vehicle approach alert device on the vehicle and a sound isolation property of the vehicle.